Dif between Pentration and Ignore (Help Wanted)
Question: What is dif between armour pent. and ignore like a 
compare 2 a 
2 Comments
Ignoring armor or magic resistance is equivalent to armor or magic penetration.
Abyssal scepter and black cleaver are not penetration items -- they are reduction items. The other items that "ignore" defences are penetration items.
The difference between them is reduction happens before penetration. This means a champion with a void staff will ignore less magic resistance if the target is affected by the abyssal scepter aura. To be exact, they will ignore 10.5 magic resistance when an enemy target has 30 magic resistance but only 3.5 magic resistance when an enemy is affected by the abyssal scepter (bringing them to 10 magic resistance.)